The vision of transmigration that closes Plato's Republic describes the souls of Homeric heroes choosing the form of their next existence, which Plato calls a "daimon". This daimon can be a person, or an animal, or even an inanimate object. As in Ovid's Metamorphoses , souls live on, transmogrified, in "all kinds of mixtures". Legends about the Hindu gods, like the myths of the Olympians, permutate multiplying selves, gender switches and phantom likenesses: transformations of the self depend on an idea of souls migrating from one shape or species to another.

Today, developments in biology, stem-cell research and genetic engineering have repositioned the concept of metamorphosis within a practical arena: the flower of immortal life that Gilgamesh brought back from the underworld, the ointment of youth and beauty that Psyche fetched for Venus, are no longer the sheer stuff of fairy tales, in an era of Michael Jackson's face, genetically modified tomatoes, middle-aged first-time mothers.

Contemporary culture revels in the potential of metamorphosis as a curse or a boon: mutants, replicants, monsters, aliens, cyborgs and a rich variety of other quasi-scientific life forms teem in comic strips, films, video games and genre fiction for adults and children. The tendency isn't confined to popular media or to sci-fi and cyberpunk: several esteemed writers of literary fiction, such as Margaret Atwood and Toni Morrison, the Canadian poet Anne Carson and the French novelist Marie Darieussecq adopt a magical model of psychology, which allows one person to take possession of another, to make huge leaps across time, to shape-shift.

In contemporary fiction, Philip Pullman has woven metamorphosis into the concept of the self in the trilogy His Dark Materials , re-imagining the Platonic daimon as a personal animal familiar that accompanies every character. These external doubles, with a life of their own as well as a symbiotic, vital connection to their "owners", have a shape-shifting character.

Children who are divided from their daemons in the course of Pullman's plot become zombies: he uses the word, which entered the English language in 1819, according to the OED. The idea of a zombie was an early 19th-century import from West Africa via the Caribbean, through the diaspora brought about by the traffic in human beings.

Zombies used to be primarily victims of voodoo masters. Today, it's become an existential term, about mental and physical enslavement, a deathly modern variation on the age-old theme of metamorphosis. Researching my new book on growing stories of metamorphosis, possession or soul-theft, I went to the British Library to look up the passage cited in the OED for zombie's English-language debut: Robert Southey's History of Brazil . I found that the British Library's copy had actually been presented by Southey to Samuel Taylor Coleridge, his friend and brother-in-law, and that Coleridge had made notes on it.

Southey is recounting the terrible revenge taken by the Spanish in 1694 on a group of escaped slaves who had established their own community, ruled by an elected chief, "chosen for his justice as well as his valour... it is said that no conspiracies or struggles for power had ever been known among them. Perhaps a feeling for religion contributed to this obedience; for zombi, the title whereby he was called, is the name for the Deity, in the Angolan tongue". Southey then added a note that "the word means Devil in their language".

In the margin, Coleridge comments that Southey is wrong to assert that zombie means "the devil". No, he writes, it means a devil, in the sense of a daimon, or indwelling vital principle.

Finding Coleridge's neat pencil annotation against the word zombi gave me a frisson. It makes such sense with his obsessions, with the entranced and spellbound figures in his most famous poems. For with regard to the modern idea that a living person can lose all power over his or her being, that the soul or inner core can die while the body remains alive, it is Coleridge who makes the first declared link between the West Indies and a new psychology of the supernatural when he writes that he was influenced by his readings about spirit cults in the Caribbean and North America. In "The Rime of the Ancient Mariner", the Mariner is a stricken, enthralled automaton; the doomed ship moves, bewitched, laden with its "ghastly crew", all of them living dead whose sounds and terrible, accursed looks deepen the Mariner's own spellbound state.

William Empson linked the Ancient Mariner to Coleridge's anti-slavery stand in the years he was writing the poem: the extreme, anguished guilt the Mariner feels arises from Coleridge's view of the personal effects of public wrongdoing. The Ancient Mariner, Empson wrote, is "the great ballad of maritime expansion and empire".

Zombies as we know them today arrived by another route from the Caribbean, however, through travellers' reports and the films they inspired: White Zombie (1932), for instance, is an early gothic nasty, in which Bela Lugosi plays the zombie master, known as "Murder" Legendre; he hammed it up, in diabolical make-up - widow's peak wig, beetling brows - with sinister close-ups of his hypnotic eyes, through which he bends his victims to his desires.

The film was influenced by The Magic Island, a first-person account of voodoo rituals written by William B Seabrook, an Englishman living in Haiti. His often lurid book had first inspired a play, simply called Zombie; when the makers of White Zombie announced their film later that same year, the playwright sued, saying he owned the concept. His suit was thrown out, the law deciding that zombies by this time belonged in the public domain.

Eleven years later, another B-movie, also destined for cult status, I Walked with a Zombie, reworked the plot of Jane Eyre, with the "madwoman in the attic" played as a beautiful, dumb, spellbound voodoo victim. The film, directed by Jacques Tourneur, sets the story on an imaginary Caribbean island, and may well lie behind Jean Rhys's ingenious reworking of Jane Eyre in Wide Sargasso Sea in 1967. But the movie that sealed the appropriation of the zombie for white consciousness was - is - The Night of the Living Dead, made in 1968 in Pittsburgh, once the great steel capital of America. By then, the mills were closing and Pittsburgh was facing decline; the team of George Romero and John Russo recast the Caribbean living dead as a ravening, restless, superannuated white proletariat rising up, under the effect of a radiation leak, to contaminate all with their condition.

So the zombie first appears in English culture as a terrifying new possibility at the peak of commercial and industrial power, when slavery was providing labour across the empire. The Death-in-Life in which the zombie exists stands at the very opposite pole from individualist, self-propelled metamorphosis of upward social mobility, which promises, as the credit card advert claims, "you can be whatever you want to be".

· Marina Warner's Fantastic Metamorphoses, Other Worlds is published by OUP. Her latest book, a collection of short stories, Murderers I Have Known, is published by Chatto and Windus on November 7. Metamorphing, examining bodily transformation in mythology, art and science, curated by Marina Warner and Sarah Bakewell, can be seen at the Science Museum, London, until February 16.